Compensator for x-ray systems



Jan. 20, 1953 R. 1 WRIGHT 2,626,360

COMPENSATOR FOR X-RAY SYSTEMS Filed July 12, 195o ATTORNEY Patented Jan. 20, 1953 UNITED STATES PATENT OFFICE COMPENSATOR FOR X-RAY SYSTEMS Vania Application July 12, 1950, Serial No. 173,263

(Cl. Z50-97) 3 claims.

The present invention relates to X-ray apparatus and more particularly to a system for maintaining a constancy of current at all kilovoltage settings for the X-ray tube and regardless of the time period during which the X-ray tube is energized.

In all X-ray systems it is of course customary to stabil-ize the X-ray tube current during an exposure by maintaining the X-ray tube filament current constant. However, upon an increase in the kilovoltage supplied to the X-ray tube the milliamperage passing through the tube will also increase. In automatic controls which are intended to cause the same milliamperage to pass through the X-ray tube at a preselected setting there is a decided disadvantage to the operation of such automatic -controls especially at short exposure periods. For example, these contr-cls look at the milliamperage and finding it too high at high kilovoltage or too low at low kilovoltage, cause an adjustment of the X-ray tube filament current until the milliamperage desired through the X-ray tube is correct for that at which it was preset to take an exposure or treat a particular part of the anatomy.

Unfortunately, however, for short exposures ranging from about one-twentieth to one-one hundred and twentieth of a second the automatic control does not operate sufliciently rapid enough to make the necessary correction during these short exposure times. This is because the controls require one cy-cle (1,430 of a second) to read the milliamperage, one cycle to apply a c-orrection and another cycle for the correction to become eiective to adjust the X-ray tube lament temperature.

It is accordingly the object of the present invention to provide an X-ray system in which the X-ray tube lament current is adjusted before the X-ray exposure is started and wherein the milliamperage of the current lowing through the X-ray tube is subsequently maintained constant at its preselected Value for all values of kilovoltage.

Another object of the present invention is the provision of an X-ray system in which the controls may be preset for any desired milliam-perage and kilovoltage and regardless of the shortness of the exposure period the milliamperage will remain constant at all values of kilovoltage.

A further object of the present invention is the provision of an X-ray system in which compensation is made for the otherwise inherent characteristic of the milliamperage increasing or decreasing with like changes in applied kilo- Voltage, so that the milliamperage is maintained constant at all values of kilovoltage by varying' the X-ray tube filament temperature.

Still further objects of the present invention will become apparent to those skilled in the art by reference to the accompanying drawing wherein the single ligure is a diagrammati-cal illustration of an X-ray system in accordance with the present invention.

Referring now to the drawing in ldetail an,

auto-transformer 5 is shown adj u-stably connected to a source of the usual commercial potential L1- L2 of 115-230 volts, by means of a switch 6. A high potential transformer 'I has its primary winding iadjustably connected to the autotransformer 5 so that the voltage supplied to transformer 'I upon closure of an exposure switch 9 determines the kilovoltage applied to the X-ray tube Iii. As will be noted, the high voltage secondary winding I2 of high tension transformer I is grounded at its cen-ter and connected through the customary full-wave rectier arrangement I3 to the X-ray tube IU, although this full wave rectifier may be omitted if desired. The lamentary cathode of the X-ray tube Il) receives heating current from the low-voltage secondary winding I4 of a transformer I5, the primary winding I6 of which is connected to designated taps on auto-transformer l through a variable impedance, such as the A. C. windings I1 of a saturable reactor I8.

This impedance has la direct current winding I9 connected to one side B-lof a direct current source of constant potential while the other end of such winding I9 is connected through a gridcontrolled discharge device 20 and a variable resistance 22, to the negative C- end of the D, C. supply source, with the cathode of the ydischarge device 2li being grounded at G. The variable-arm 23 of resistance 22 connects through a portion of a further variable resistance 24 and the adjustable arm 25 thereof to the grid electrode of the discharge device 2e so that once the arm 23 is set for a preselected voltage ydrop across resistance 22 a negative bias of predetermined magnitude is impressed on the grid relative to the cathode of the discharge device 26.

In order to compensate for a variation in the milliamperage upon an increase or decrease in kilovoltage, a transformer 2B is provided having its primary winding 2l parallel with primary winding 8 of high potential transformer 'I but connected ahead of exposure switch 9 so that the primary winding 21 is energized from autotransformer 'I prior to the making of an exposure by closure of switch 8. The secondary winding 28 has its ends connected to the respective anodes of a full wave rectier tube 29 while the center tap of such secondary winding 28 is connected to the cathode of the recter tube 29, through a lter circuit comprising a parallel connected capacitor 30 and the variable resistance 211.

In the operation of the system of the present invention the adjustable arm 23 of variable resistance 22 is set for a given installation. The constant voltage D. C. supply source will accordingly apply a voltage to the D. C. winding I9 of the saturable reactor depending upon the negative bias applied to the control grid of the discharge device 2li, to influence the current flowingthrough the A. C. windings Il thus maintaining the X-ray tube illament at a fixed tempera-ture which controls the milliamperage through the X-ray tube l D during a subsequent exposure.

To compensate for the otherwise inherent tendency of the milliamperage to vary with changes in kilovoltage, the unidirectional current supplied by transformer 26 and rectified by rectier 29, causes a slight variation in the negative bias applied to the grid of the discharge device 28 by the portion of variable resistance 24 connected in series with the grid. For example, the two sections of the secondary` winding 2i! generate a maximum of about 6 volts each at the maximum kilovoltage setting of the controls on auto-transformer 1. This in turn, at high kilovoltage, causes the portion of variable resistance 2t to apply a slightly more negative bias (a few tenths of a volt) on the grid of discharge device 29 than at lower kilovoltage. This accordingly makes the X-ray tube lament temperature lower at high kilovoltage setting than at lower kilovoltage and by proper adjustment of the variable resistance arm the X-ray tube lament temperature is in turn adjusted so that a desired constant milliamperage is obtained through the X-ray tube at all values of kilovoltage. Moreover, since the compensating arrangement including transformer' 26 is connected ahead of the high tension transformer primary 8, all adjustments are conveniently made prior to an exposure and constancy of m-illiamperage at all values of kilovoltage is thus assured, regardless of the shortness of time period of the subsequent exposure.

It should thus become obvious to those skilled in the art that an X-ray system is provided by the present invention wherein compensation is made for otherwise variation in milliamperage through the X-ray tube with changes in kilovoltage applied to such tube, so that a constant milliamperage isl assured at all kilovoltage settings. Moreover, the compensator operates to condition the system for such assurance prior to the actual making of an exposure.

Although one specific embodiment of the present invention has been shown and described, it is to be understood that still further modication thereof may be made without departing from the spirit and scope of the appended claims.

IY claim:

1. An X-ray system for maintaining constancy of milliamperage through an X-ray tube at all kilovoltage settings during the making of short exposures comprising an X-ray tube energizable from a source of supply including a high potential transformer and provided with a thermionic cathode, a source of heating energy for said thermionic cathode including a variable impedance, a control circuit for said variable impedance including a discharge device provided with a control electrode, and means comprising a transformer having its primary winding connected to the same source of supply in electrical parallel with the high potential transformer for said X-ray tube and energizable from said source prior to energization of said X-ray tube for the making of a short exposure, and said means including a rectier tube connected to said transformer and a iiltcr arrangement connected to the output of said rectiiier and to the control electrode of said discharge device and operable to apply a predetermined voltage to the latter which varies with direct changes in kilovoltage setting to control said variable impedance with an attendant predetermined control of the temperature of the thermionic cathode and said X-ray tube and to prevent variation of the milliamperage through the latter at all values of kilovoltage applied to said X-ray tube.

2. An X-ray system for maintaining constancy of milliamperage through an X-ray tube at all kilovoltage settings during the making of short exposures comprising an X-ray tube energizable from a source of supply including a high potential transformer and provided with a thermionic cathode, a source of heating energy for said thermionic cathode including a saturable reactor provided with a direct-current winding and an alternating current winding in series with the source of heating energy, a source of direct-current for the direct-current winding of said saturable reactor including a discharge device provided with a control electrode, and means connected to the same source of supply in electrical parallel with the high potential transformer for said X-ray tube and energizable therefrom prior to energization of said X-ray tube for the making of a short exposure, said means including a rectified source of electrical energy operable to apply a predetermined voltage to the control electrode of said discharge device which varies with direct changes in kilovoltage setting to regulate the electrical energy supplied to the direct-current winding of said saturable reactor with an attendant regulation of the electrical energy owing through the alternating current windings to predetermine the temperature of the thermionic cathode of said X-ray tube and prevent variation of the milliamperage through the latter at all values of kilovoltage applied to said X-ray tube.

3. An X-ray system for maintaining constancy of milliamperage through an X-ray tube at all kilovoltage settings during the making of short exposures comprising an X-ray tube energizable from a source of supply including a high potential transformer and provided with a thermionic cathode, a source of heating energy for said thermionic cathode including a saturable reactor provided with a direct-current winding and an alternating current winding in series with the source of heating energy, a source of directcurrent for the direct-current winding of said saturable reactor including a discharge device provided with a control electrode, and means comprising a transformer connected to the same source of supply in electrical parallel with the high potential transformer for said X-ray tube and energizable from said source prior to energization of said X-ray tube for the making of a short exposure, and said means including a rectii'ler tube connected to said transformer and a lter arrangement connected to the output of said rectifier and to the control electrode of said discharge device and operable to apply a predetermined voltage to the latter which varies 5 6 with direct changes in klovoltage setting to REFERENCES CITED regulate the electrical energy Supplied t0 the The following references are of record in the directecurrent winding of said saturable reactor fue of this patent: with an attendant regulation of the electrical energy owng through the alternating current 5 UNITED STATES PATENTS windings to predetermine the temperature of the Number Name Date thermonc cathode of said X-ray tube and pre- 1,870,937 Werner Aug. 9, 1932 vent Variation of the milliamperage through the 2,319,378 Weisglass May 18, 1943 latter at all values of kilovoltage applied to said 2,494,218 Weisglass Jan. 10, 1950 X-ray tube. 10 2,512,193 Zavales June 20, 1950 ROBERT L. WRIGHT. 2,514,935 Clapp July 1l, 1950 

